Method and systems for the delivery of oxygen enriched gas

ABSTRACT

Described herein are various embodiments of an oxygen concentrator system and method of delivering oxygen enriched gas to a user. In some embodiments, oxygen concentrator system includes one or more components that improve the efficiency of oxygen enriched gas delivery during operation of the oxygen concentrator system.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application Ser.No. 61/713,254 entitled “Oxygen Concentrator Systems and Methods forOral Delivery of Oxygen Enriched Air” filed Oct. 12, 2012, which isincorporated herein by reference in its entirety; and U.S. ProvisionalApplication Ser. No. 61/804,365 entitled “Method and Systems for theDelivery of Oxygen Enriched Gas” filed Mar. 22, 2013, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and system thatprovide oxygen enriched gas to a subject.

2. Description of the Related Art

There are many patients that require supplemental oxygen as part of LongTerm Oxygen Therapy (LTOT). Currently, the vast majority of patientsthat are receiving LTOT are diagnosed under the general category ofChronic Obstructive Pulmonary Disease, COPD. This general diagnosisincludes such common diseases as Chronic Asthma, Emphysema, CongestiveHeart Failure and several other cardio-pulmonary conditions. Otherpeople (e.g., obese individuals) may also require supplemental oxygen,for example, to maintain elevated activity levels.

Doctors may prescribe oxygen concentrators or portable tanks of medicaloxygen for these patients. Usually a specific oxygen flow rate isprescribed (e.g., 1 liter per minute (LPM), 2 LPM, 3 LPM, etc.). Expertsin this field have also recognized that exercise for these patientsprovide long term benefits that slow the progression of the disease,improve quality of life and extend patient longevity. Most stationaryforms of exercise like tread mills and stationary bicycles, however, aretoo strenuous for these patients. As a result, the need for mobility haslong been recognized. Until recently, this mobility has been facilitatedby the use of small compressed oxygen tanks. The disadvantage of thesetanks is that they have a finite amount of oxygen and they are heavy,weighing about 50 pounds, when mounted on a cart with dolly wheels.

Oxygen concentrators have been in use for about 50 years to supplypatients suffering from respiratory insufficiency with supplementaloxygen. Traditional oxygen concentrators used to provide these flowrates have been bulky and heavy making ordinary ambulatory activitieswith them difficult and impractical. Recently, companies thatmanufacture large stationary home oxygen concentrators began developingportable oxygen concentrators, POCs. The advantage of POCs concentratorswas that they can produce a theoretically endless supply of oxygen. Inorder to make these devices small for mobility, the various systemsnecessary for the production of oxygen enriched gas are condensed.

SUMMARY

Systems and methods of providing an oxygen enriched gas to a user of anoxygen concentrator are described herein.

In one embodiment, a method of providing oxygen enriched gas to a userof an oxygen concentrator, includes: measuring the time between at leastthree successive breaths, wherein a breath is determined to begin when adrop in pressure is measured using a pressure sensor coupled to anoutlet of a conduit coupling the user to an oxygen enriched gas source;determining an average breathing rate based on the time between each ofthe successive breaths, wherein the time between the penultimate breathand the last breath is not used to determine the average breathing rate;and setting an inspiration breath pressure threshold for the pressuresensor based on the determined average breathing rate. In an embodiment,the time is measured between six successive breaths. Adjusting theinspiration breath pressure threshold based on the average breathingrate, in some embodiments, is performed automatically. The oxygenenriched gas source may be an oxygen concentrator system or an oxygentank.

In some embodiments, the threshold inspiration pressure is lowered whenthe determined average breathing rate changes from greater than 10breaths per minute to less than 10 breaths per minute. In someembodiments, the threshold inspiration pressure is increased when thedetermined average breathing rate changes from less than 15 breaths perminute to greater than 15 breaths per minute. The inspiration breathpressure threshold may be maintained at a current setting when theaverage breathing rate is between about 10 breaths per minute and about15 breaths per minute.

In some embodiments, the method further includes switching to an activemode, a sedentary mode, or remaining at the current mode based on theaverage breathing rate. For example, an active mode may be implementedwhen the average breathing rate comprises at least 15 breaths perminute. A sedentary mode may be activated when the average breathingrate comprises less than 10 breaths per minute.

In an embodiment, an oxygen concentrator apparatus includes: a pressuresensor, the pressure sensor configured to detect a breath pressure of auser; and a processor operable coupled to the pressure sensor. Theprocessor is capable of executing non-transitory program instructions,wherein the program instructions are operable to: automatically measurethe time between at least three successive breaths, wherein a breath isdetermined to begin when a drop in pressure is measured using thepressure sensor; determine an average breathing rate based on the timebetween each of the successive breaths, wherein the time between thepenultimate breath and the last breath is not used to determine theaverage breathing rate; and set an inspiration breath pressure thresholdfor the pressure sensor based on the determined average breathing rate.

In another embodiment, a method of providing oxygen enriched gas to auser of an oxygen concentrator includes: determining a ratio of thechange in absolute pressure during inhalation with respect to time,monitored over at least three breaths, wherein inhalation is determinedto begin when a drop in pressure is measured using a pressure sensorcoupled to an outlet of a conduit coupling the user to an oxygenenriched gas source; and adjusting an inspiration breath pressurethreshold of the breath pressure sensor based on the ratio of the changein absolute pressure with respect to time. When determining the ratio,in some embodiments, the change in absolute pressure of the last breathis not used to determine the ratio. The oxygen enriched gas source maybe an oxygen concentrator system or an oxygen tank.

Adjusting an inspiration breath pressure threshold of the pressuresensor based on the ratio includes adjusting the inspiration breathpressure threshold to a lower inspiration threshold breath pressurerelative to a current inspiration breath pressure threshold if the ratiois negative. In an embodiment, adjusting an inspiration breath pressurethreshold of the pressure sensor based on the ratio includes adjustingthe inspiration breath pressure threshold to a lower inspirationthreshold breath pressure relative to a current inspiration breathpressure threshold if the ratio is negative and less than or equal to−0.5.

Adjusting an inspiration breath pressure threshold of the pressuresensor based on the ratio includes adjusting the inspiration breathpressure threshold to a higher inspiration threshold breath pressurerelative to a current inspiration breath pressure threshold if the ratiois positive. In an embodiment, adjusting an inspiration breath pressurethreshold of the pressure sensor based on the ratio includes adjustingthe inspiration breath pressure threshold to a higher inspirationthreshold breath pressure relative to a current inspiration breathpressure threshold if the ratio is positive and greater than or equal to−0.5.

In some embodiments, the method further includes switching to an activemode, a sedentary mode, or remaining at the current mode based on theaverage breathing rate. For example, an active mode may be implementedwhen the ratio is positive. A sedentary mode may be activated when theratio is negative.

In an embodiment, an oxygen concentrator apparatus includes: a pressuresensor configured to detect a breath pressure of a user; and a processorcoupled to the pressure sensor. The processor is capable of executingnon-transitory program instructions, wherein the program instructionsare operable to: determine of a ratio of the change in absolute pressureduring inhalation with respect to time, monitored over at least threebreaths, wherein inhalation is determined to begin when a drop inpressure is measured using a pressure sensor coupled to an outlet of aconduit coupling the user to an oxygen enriched gas source; and adjustan inspiration breath pressure threshold of the breath pressure sensorbased on the ratio of the change in absolute pressure with respect totime.

In an embodiment, a method of providing oxygen enriched gas to a user ofan oxygen concentrator, includes: measuring the time between a pluralityof successive breaths, wherein a breath is determined to begin when adrop in pressure is measured using a pressure sensor coupled to anoutlet of a conduit coupling the user to an oxygen enriched gas source;creating groupings of breaths, wherein each grouping comprises at leastthree successive breaths; determining an average breathing rate for eachgrouping based on the time between each of the successive breaths withinthe grouping; and setting an inspiration breath pressure threshold forthe pressure sensor based on the determined average breathing rate oftwo or more of the groupings.

In an embodiment, a method of providing oxygen enriched gas to a user ofan oxygen concentrator, includes: measuring the time between a pluralityof successive breaths, wherein a breath is determined to begin when adrop in pressure is measured using a pressure sensor coupled to anoutlet of a conduit coupling the user to an oxygen enriched gas source;determining an average time between each of the successive breaths forat least three successive breaths, wherein the time between thepenultimate breath and the last breath is not used to determine theaverage time; and setting an inspiration breath pressure threshold forthe pressure sensor based on the determined average time.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to thoseskilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which:

FIG. 1 depicts a schematic diagram of an embodiment of the components ofan oxygen concentrator;

FIG. 2 depicts a schematic diagram of an embodiment of the outletcomponents of an oxygen concentrator;

FIG. 3 depicts a schematic diagram of an embodiment of an outlet conduitfor an oxygen concentrator;

FIG. 4 depicts a perspective view of an embodiment of a dissembledcanister system;

FIG. 5 depicts a perspective view of an embodiment of an end of acanister system;

FIG. 6 depicts the assembled end of an embodiment of the canister systemend depicted in FIG. 5;

FIG. 7 depicts a perspective view of an embodiment of an opposing end ofthe canister system depicted in FIGS. 4 and 5;

FIG. 8 depicts a perspective view of an embodiment of the assembledopposing end of the canister system end depicted in FIG. 7;

FIG. 9 depicts various profiles of embodiments for providing oxygenenriched gas from an oxygen concentrator; and

FIG. 10 depicts a flow-chart of a process for adjusting the inspirationbreath pressure threshold.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION

It is to be understood the present invention is not limited toparticular devices or methods, which may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. Headings are for organizational purposes only and are notmeant to be used to limit or interpret the description or claims. Asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include singular and plural referents unless thecontent clearly dictates otherwise. Furthermore, the word “may” is usedthroughout this application in a permissive sense (i.e., having thepotential to, being able to), not in a mandatory sense (i.e., must). Theterm “include,” and derivations thereof, mean “including, but notlimited to.”

The term “coupled” as used herein means either a direct connection or anindirect connection (e.g., one or more intervening connections) betweenone or more objects or components. The phrase “connected” means a directconnection between objects or components such that the objects orcomponents are connected directly to each other. As used herein thephrase “obtaining” a device means that the device is either purchased orconstructed.

Oxygen concentrators take advantage of pressure swing adsorption (PSA).Pressure swing adsorption involves using a compressor to increase gaspressure inside a canister that contains particles of a gas separationadsorbent. As the pressure increases, certain molecules in the gas maybecome adsorbed onto the gas separation adsorbent. Removal of a portionof the gas in the canister under the pressurized conditions allowsseparation of the non-adsorbed molecules from the adsorbed molecules.The gas separation adsorbent may be regenerated by reducing thepressure, which reverses the adsorption of molecules from the adsorbent.Further details regarding oxygen concentrators may be found, forexample, in U.S. Published Patent Application No. 2009-0065007,published Mar. 12, 2009, and entitled “Oxygen Concentrator Apparatus andMethod”, which is incorporated herein by reference.

Ambient air usually includes approximately 78% nitrogen and 21% oxygenwith the balance comprised of argon, carbon dioxide, water vapor andother trace elements. If a gas mixture such as air, for example, ispassed under pressure through a vessel containing a gas separationadsorbent bed that attracts nitrogen more strongly than it does oxygen,part or all of the nitrogen will stay in the bed, and the gas coming outof the vessel will be enriched in oxygen. When the bed reaches the endof its capacity to adsorb nitrogen, it can be regenerated by reducingthe pressure, thereby releasing the adsorbed nitrogen. It is then readyfor another cycle of producing oxygen enriched air. By alternatingcanisters in a two-canister system, one canister can be collectingoxygen while the other canister is being purged (resulting in acontinuous separation of the oxygen from the nitrogen). In this manner,oxygen can be accumulated out of the air for a variety of uses includeproviding supplemental oxygen to patients.

FIG. 1 illustrates a schematic diagram of an oxygen concentrator 100,according to an embodiment. Oxygen concentrator 100 may concentrateoxygen out of an air stream to provide oxygen enriched gas to a user. Asused herein, “oxygen enriched gas” is composed of at least about 50%oxygen, at least about 60% oxygen, at least about 70% oxygen, at leastabout 80% oxygen, at least about 90% oxygen, at least about 95% oxygen,at least about 98% oxygen, or at least about 99% oxygen.

Oxygen concentrator 100 may be a portable oxygen concentrator. Forexample, oxygen concentrator 100 may have a weight and size that allowsthe oxygen concentrator to be carried by hand and/or in a carrying case.In one embodiment, oxygen concentrator 100 has a weight of less thanabout 20 lbs., less than about 15 lbs., less than about 10 lbs., or lessthan about 5 lbs. In an embodiment, oxygen concentrator 100 has a volumeof less than about 1000 cubic inches, less than about 750 cubic inches;less than about 500 cubic inches, less than about 250 cubic inches, orless than about 200 cubic inches.

Oxygen may be collected from ambient air by pressurizing ambient air incanisters 302 and 304, which include a gas separation adsorbent. Gasseparation adsorbents useful in an oxygen concentrator are capable ofseparating at least nitrogen from an air stream to produce oxygenenriched gas. Examples of gas separation adsorbents include molecularsieves that are capable of separation of nitrogen from an air stream.Examples of adsorbents that may be used in an oxygen concentratorinclude, but are not limited to, zeolites (natural) or syntheticcrystalline aluminosilicates that separate nitrogen from oxygen in anair stream under elevated pressure. Examples of synthetic crystallinealuminosilicates that may be used include, but are not limited to:OXYSIV adsorbents available from UOP LLC, Des Plaines, Iowa; SYLOBEADadsorbents available from W. R. Grace & Co, Columbia, Md.; SILIPORITEadsorbents available from CECA S.A. of Paris, France; ZEOCHEM adsorbentsavailable from Zeochem AG, Uetikon, Switzerland; and AgLiLSX adsorbentavailable from Air Products and Chemicals, Inc., Allentown, Pa.

As shown in FIG. 1, air may enter the oxygen concentrator through airinlet 106. Air may be drawn into air inlet 106 by compression system200. Compression system 200 may draw in air from the surroundings of theoxygen concentrator and compress the air, forcing the compressed airinto one or both canisters 302 and 304. In an embodiment, an inletmuffler 108 may be coupled to air inlet 106 to reduce sound produced byair being pulled into the oxygen generator by compression system 200. Inan embodiment, inlet muffler 108 may be a moisture and sound absorbingmuffler. For example, a water absorbent material (such as a polymerwater absorbent material or a zeolite material) may be used to bothabsorb water from the incoming air and to reduce the sound of the airpassing into the air inlet 106.

Compression system 200 may include one or more compressors capable ofcompressing air. In some embodiments, compression system may includeone, two, three, four, or more compressors. Compression system 200 asdepicted that includes compressor 210 and motor 220. Motor 220 iscoupled to compressor 210 and provides an operating force to thecompressor to operate the compression mechanism. Pressurized air,produced by compression system 200, may be forced into one or both ofthe canisters 302 and 304. In some embodiments, the ambient air may bepressurized in the canisters to a pressure approximately in a range of13-20 pounds per square inch (psi). Other pressures may also be used,depending on the type of gas separation adsorbent disposed in thecanisters.

In some embodiments, motor 220 is coupled to a pressurizing device (e.g.piston pump or a diaphragm pump). The pressuring device may be a pistonpump that has multiple pistons. During operation, the pistons may beselectively turned on or off. In some embodiments, motor 220 may becoupled to multiple pumps. Each pump may be selectively turned on oroff. For example, controller 400 may determine which pumps or pistonsshould be operated based on predetermined operating conditions.

Coupled to each canister 302/304 are inlet valves 122/124 and outletvalves 132/134. As shown in FIG. 1, inlet valve 122 is coupled tocanister 302 and inlet valve 124 is coupled to canister 304. Outletvalve 132 is coupled to canister 302 and outlet valve 134 is coupled tocanister 304. Inlet valves 122/124 are used to control the passage ofair from compression system 200 to the respective canisters. Outletvalves 132/134 are used to release gas from the respective canistersduring a venting process. In some embodiments, inlet valves 122/124 andoutlet valves 132/134 may be silicon plunger solenoid valves. Othertypes of valves, however, may be used. Plunger valves offer advantagesover other kinds of valves by being quiet and having low slippage.

In some embodiments, a two-step valve actuation voltage may be used tocontrol inlet valves 122/124 and outlet valves 132/134. For example, ahigh voltage (e.g., 24 V) may be applied to an inlet valve to open theinlet valve. The voltage may then be reduced (e.g., to 7 V) to keep theinlet valve open. Using less voltage to keep a valve open may use lesspower (Power=Voltage*Current). This reduction in voltage minimizes heatbuildup and power consumption to extend run time from the battery. Whenthe power is cut off to the valve, it closes by spring action. In someembodiments, the voltage may be applied as a function of time that isnot necessarily a stepped response (e.g., a curved downward voltagebetween an initial 24 V and a final 7 V).

In some embodiments, air may be pulled into the oxygen concentratorthrough compressors 305, 310. In some embodiments, air may flow fromcompressors 305, 310 to canisters 302, 304. In some embodiments, one ofvalves 122 or 124 may be closed (e.g., as signaled by controller 400)resulting in the combined output of both compressors 305, 310 lowingthrough the other respective valve 122 or 124 into a respective canister302, 304. For example, if valve 124 is closed, the air from bothcompressors 305, 310 may flow through valve 122. If valve 122 is closed,the air from both compressors 305, 310 may flow through valve 124. Insome embodiments, valve 122 and valve 124 may alternate to alternatelydirect the air from the compressors 305, 310 into respective canisters302 or 304.

In an embodiment, pressurized air is sent into one of canisters 302 or304 while the other canister is being vented. For example, during use,inlet valve 122 is opened while inlet valve 124 is closed. Pressurizedair from compression system 200 is forced into canister 302, while beinginhibited from entering canister 304 by inlet valve 124. In anembodiment, a controller 400 is electrically coupled to valves 122, 124,132, and 134. Controller 400 includes one or more processors 410operable to execute program instructions stored in memory 420. Theprogram instructions are operable to perform various predefined methodsthat are used to operate the oxygen concentrator. Controller 400 mayinclude program instructions for operating inlet valves 122 and 124 outof phase with each other, i.e., when one of inlet valves 122 or 124 isopened, the other valve is closed. During pressurization of canister302, outlet valve 132 is closed and outlet valve 134 is opened. Similarto the inlet valves, outlet valves 132 and 134 are operated out of phasewith each other. In some embodiments, the voltages and the duration ofthe voltages used to open the input and output valves may be controlledby controller 400.

Check valves 142 and 144 are coupled to canisters 302 and 304,respectively. Check valves 142 and 144 are one way valves that arepassively operated by the pressure differentials that occur as thecanisters are pressurized and vented. Check valves 142 and 144 arecoupled to canisters to allow oxygen produced during pressurization ofthe canister to flow out of the canister, and to inhibit back flow ofoxygen or any other gases into the canister. In this manner, checkvalves 142 and 144 act as one way valves allowing oxygen enriched gas toexit the respective canister during pressurization.

The term “check valve”, as used herein, refers to a valve that allowsflow of a fluid (gas or liquid) in one direction and inhibits back flowof the fluid. Examples of check valves that are suitable for useinclude, but are not limited to: a ball check valve; a diaphragm checkvalve; a butterfly check valve; a swing check valve; a duckbill valve;and a lift check valve. Under pressure, nitrogen molecules in thepressurized ambient air are adsorbed by the gas separation adsorbent inthe pressurized canister. As the pressure increases, more nitrogen isadsorbed until the gas in the canister is enriched in oxygen. Thenonadsorbed gas molecules (mainly oxygen) flow out of the pressurizedcanister when the pressure reaches a point sufficient to overcome theresistance of the check valve coupled to the canister. In oneembodiment, the pressure drop of the check valve in the forwarddirection is less than 1 psi. The break pressure in the reversedirection is greater than 100 psi. It should be understood, however,that modification of one or more components would alter the operatingparameters of these valves. If the forward flow pressure is increased,there is, generally, a reduction in oxygen enriched gas production. Ifthe break pressure for reverse flow is reduced or set too low, there is,generally, a reduction in oxygen enriched gas pressure.

In an exemplary embodiment, canister 302 is pressurized by compressedair produced in compression system 200 and passed into canister 302.During pressurization of canister 302 inlet valve 122 is open, outletvalve 132 is closed, inlet valve 124 is closed and outlet valve 134 isopen. Outlet valve 134 is opened when outlet valve 132 is closed toallow substantially simultaneous venting of canister 304 while canister302 is pressurized. Canister 302 is pressurized until the pressure incanister is sufficient to open check valve 142. Oxygen enriched gasproduced in canister 302 exits through check valve and, in oneembodiment, is collected in accumulator 106.

After some time the gas separation adsorbent will become saturated withnitrogen and will be unable to separate significant amounts of nitrogenfrom incoming air. This point is usually reached after a predeterminedtime of oxygen enriched gas production. In the embodiment describedabove, when the gas separation adsorbent in canister 302 reaches thissaturation point, the inflow of compressed air is stopped and canister302 is vented to remove nitrogen. During venting, inlet valve 122 isclosed, and outlet valve 132 is opened. While canister 302 is beingvented, canister 304 is pressurized to produce oxygen enriched gas inthe same manner described above. Pressurization of canister 304 isachieved by closing outlet valve 134 and opening inlet valve 124. Theoxygen enriched gas exits canister 304 through check valve 144.

During venting of canister 302, outlet valve 132 is opened allowingpressurized gas (mainly nitrogen) to exit the canister throughconcentrator outlet 130. In an embodiment, the vented gases may bedirected through muffler 133 to reduce the noise produced by releasingthe pressurized gas from the canister. As gas is released from canister302, pressure in the canister drops. The drop in pressure may allow thenitrogen to become desorbed from the gas separation adsorbent. Thereleased nitrogen exits the canister through outlet 130, resetting thecanister to a state that allows renewed separation of oxygen from an airstream. Muffler 133 may include open cell foam (or another material) tomuffle the sound of the gas leaving the oxygen concentrator. In someembodiments, the combined muffling components/techniques for the inputof air and the output of gas may provide for oxygen concentratoroperation at a sound level below 50 decibels.

During venting of the canisters, it is advantageous that at least amajority of the nitrogen is removed. In an embodiment, at least about50%, at least about 60%, at least about 70%, at least about 80%, atleast about 90%, at least about 95%, at least about 98%, orsubstantially all of the nitrogen in a canister is removed before thecanister is re-used to separate oxygen from air. In some embodiments, acanister may be further purged of nitrogen using an oxygen enrichedstream that is introduced into the canister from the other canister.

In an exemplary embodiment, a portion of the oxygen enriched gas may betransferred from canister 302 to canister 304 when canister 304 is beingvented of nitrogen. Transfer of oxygen enriched gas from canister 302 to304, during venting of canister 304, helps to further purge nitrogen(and other gases) from the canister. In an embodiment, oxygen enrichedgas may travel through flow restrictors 151, 153, and 155 between thetwo canisters. Flow restrictor 151 may be a trickle flow restrictor.Flow restrictor 151, for example, may be a 0.009 D flow restrictor(e.g., the flow restrictor has a radius of 0.009 inches which is lessthan the diameter of the tube it is inside). Flow restrictors 153 and155 may be 0.013 D flow restrictors. Other flow restrictor types andsizes are also contemplated and may be used depending on the specificconfiguration and tubing used to couple the canisters. In someembodiments, the flow restrictors may be press fit flow restrictors thatrestrict air flow by introducing a narrower diameter in their respectivetube. In some embodiments, the press fit flow restrictors may be made ofsapphire, metal or plastic (other materials are also contemplated).

Flow of oxygen enriched gas is also controlled by use of valve 152 andvalve 154. Valves 152 and 154 may be opened for a short duration duringthe venting process (and may be closed otherwise) to prevent excessiveoxygen loss out of the purging canister. Other durations are alsocontemplated. In an exemplary embodiment, canister 302 is being ventedand it is desirable to purge canister 302 by passing a portion of theoxygen enriched gas being produced in canister 304 into canister 302. Aportion of oxygen enriched gas, upon pressurization of canister 304,will pass through flow restrictor 151 into canister 302 during ventingof canister 302. Additional oxygen enriched air is passed into canister302, from canister 304, through valve 154 and flow restrictor 155. Valve152 may remain closed during the transfer process, or may be opened ifadditional oxygen enriched gas is needed. The selection of appropriateflow restrictors 151 and 155, coupled with controlled opening of valve154 allows a controlled amount of oxygen enriched gas to be sent fromcanister 304 to 302. In an embodiment, the controlled amount of oxygenenriched gas is an amount sufficient to purge canister 302 and minimizethe loss of oxygen enriched gas through venting valve 132 of canister302. While this embodiment describes venting of canister 302, it shouldbe understood that the same process can be used to vent canister 304using flow restrictor 151, valve 152 and flow restrictor 153.

The pair of equalization/vent valves 152/154 work with flow restrictors153 and 155 to optimize the air flow balance between the two canisters.This may allow for better flow control for venting the canisters withoxygen enriched gas from the other of the canisters. It may also providebetter flow direction between the two canisters. It has been found that,while flow valves 152/154 may be operated as bi-directional valves, theflow rate through such valves varies depending on the direction of fluidflowing through the valve. For example, oxygen enriched gas flowing fromcanister 304 toward canister 302 has a flow rate faster through valve152 than the flow rate of oxygen enriched gas flowing from canister 302toward canister 304 through valve 152. If a single valve was to be used,eventually either too much or too little oxygen enriched gas would besent between the canisters and the canisters would, over time, begin toproduce different amounts of oxygen enriched gas. Use of opposing valvesand flow restrictors on parallel air pathways may equalize the flowpattern of the oxygen between the two canisters. Equalizing the flow mayallow for a steady amount of oxygen available to the user over multiplecycles and also may allow a predictable volume of oxygen to purge theother of the canisters. In some embodiments, the air pathway may nothave restrictors but may instead have a valve with a built in resistanceor the air pathway itself may have a narrow radius to provideresistance.

At times, oxygen concentrator may be shut down for a period of time.When an oxygen concentrator is shut down, the temperature inside thecanisters may drop as a result of the loss of adiabatic heat from thecompression system. As the temperature drops, the volume occupied by thegases inside the canisters will drop. Cooling of the canisters may leadto a negative pressure in the canisters. Valves (e.g., valves 122, 124,132, and 134) leading to and from the canisters are dynamically sealedrather than hermetically sealed. Thus, outside air may enter thecanisters after shutdown to accommodate the pressure differential. Whenoutside air enters the canisters, moisture from the outside air maycondense inside the canister as the air cools. Condensation of waterinside the canisters may lead to gradual degradation of the gasseparation adsorbents, steadily reducing ability of the gas separationadsorbents to produce oxygen enriched gas.

In an embodiment, outside air may be inhibited from entering canistersafter the oxygen concentrator is shut down by pressurizing bothcanisters prior to shut down. By storing the canisters under a positivepressure, the valves may be forced into a hermetically closed positionby the internal pressure of the air in the canisters. In an embodiment,the pressure in the canisters, at shutdown, should be at least greaterthan ambient pressure. As used herein the term “ambient pressure” refersto the pressure of the surroundings that the oxygen generator is located(e.g. the pressure inside a room, outside, in a plane, etc.). In anembodiment, the pressure in the canisters, at shutdown, is at leastgreater than standard atmospheric pressure (i.e., greater than 760 mmHg(Torr), 1 atm, 101,325 Pa). In an embodiment, the pressure in thecanisters, at shutdown, is at least about 1.1 times greater than ambientpressure; is at least about 1.5 times greater than ambient pressure; oris at least about 2 times greater than ambient pressure.

In an embodiment, pressurization of the canisters may be achieved bydirecting pressurized air into each canister from the compression systemand closing all valves to trap the pressurized air in the canisters. Inan exemplary embodiment, when a shutdown sequence is initiated, inletvalves 122 and 124 are opened and outlet valves 132 and 134 are closed.Because inlet valves 122 and 124 are joined together by a commonconduit, both canisters 302 and 304 may become pressurized as air and oroxygen enriched gas from one canister may be transferred to the othercanister. This situation may occur when the pathway between thecompression system and the two inlet valves allows such transfer.Because the oxygen generator operates in an alternatingpressurize/venting mode, at least one of the canisters should be in apressurized state at any given time. In an alternate embodiment, thepressure may be increased in each canister by operation of compressionsystem 200. When inlet valves 122 and 124 are opened, pressure betweencanisters 302 and 304 will equalize, however, the equalized pressure ineither canister may not be sufficient to inhibit air from entering thecanisters during shutdown. In order to ensure that air is inhibited fromentering the canisters, compression system 200 may be operated for atime sufficient to increase the pressure inside both canisters to alevel at least greater than ambient pressure. Regardless of the methodof pressurization of the canisters, once the canisters are pressurized,inlet valves 122 and 124 are closed, trapping the pressurized air insidethe canisters, which inhibits air from entering the canisters during theshutdown period.

An outlet system, coupled to one or more of the canisters, includes oneor more conduits for providing oxygen enriched gas to a user. In anembodiment, oxygen enriched gas produced in either of canisters 302 and304 is collected in accumulator 106 through check valves 142 and 144,respectively, as depicted schematically in FIG. 1. The oxygen enrichedgas leaving the canisters may be collected in oxygen accumulator 106prior to being provided to a user. In some embodiments, a tube may becoupled to accumulator 106 to provide the oxygen enriched gas to theuser. Oxygen enriched gas may be provided to the user through an airwaydelivery device that transfer the oxygen enriched gas to the user'smouth and/or nose. In an embodiment, an outlet may include a tube thatdirects the oxygen toward a user's nose and/or mouth that may not bedirectly coupled to the user's nose.

Turning to FIG. 2, a schematic diagram of an embodiment of an outletsystem for an oxygen concentrator is shown. Supply valve 160 may becoupled to outlet tube to control the release of the oxygen enriched gasfrom accumulator 106 to the user. In an embodiment, supply valve 160 isan electromagnetically actuated plunger valve. Supply valve 160 isactuated by controller 400 to control the delivery of oxygen enrichedgas to a user. Actuation of supply valve 160 is not timed orsynchronized to the pressure swing adsorption process. Instead,actuation is, in some embodiments, synchronized to the patient'sbreathing. Additionally, supply valve 160 may have multiple actuationsto help establish a clinically effective flow profile for providingoxygen enriched gas.

Oxygen enriched gas in accumulator 106 passes through supply valve 160into expansion chamber 170 as depicted in FIG. 2. In an embodiment,expansion chamber may include one or more devices capable of being usedto determine an oxygen concentration of gas passing through the chamber.Oxygen enriched gas in expansion chamber 170 builds briefly, throughrelease of gas from accumulator by supply valve 160, and then is bledthrough small orifice flow restrictor 175 to flow rate sensor 185 andthen to particulate filter 187. Flow restrictor 175 may be a 0.025 Dflow restrictor. Other flow restrictor types and sizes may be used. Insome embodiments, the diameter of the air pathway in the housing may berestricted to create restricted air flow. Flow rate sensor 185 may beany sensor capable of assessing the rate of gas flowing through theconduit. Particulate filter 187 may be used to filter bacteria, dust,granule particles, etc. prior to delivery of the oxygen enriched gas tothe user. The oxygen enriched gas passes through filter 187 to connector190 which sends the oxygen enriched gas to the user via conduit 192 andto pressure sensor 194.

The fluid dynamics of the outlet pathway, coupled with the programmedactuations of supply valve 160, results in a bolus of oxygen beingprovided at the correct time and with a flow profile that assures rapiddelivery into the patient's lungs without any excessive flow rates thatwould result in wasted retrograde flow out the nostrils and into theatmosphere. It has been found, in our specific system, that the totalvolume of the bolus required for prescriptions is equal to 11 mL foreach LPM, i.e., 11 mL for a prescription of 1 LPM; 22 mL for aprescription of 2 LPM; 33 mL for a prescription of 3 LPM; 44 mL for aprescription of 4 LPM; 55 mL for a prescription of 5 LPM; etc. This isgenerally referred to as the LPM equivalent. It should be understoodthat the LPM equivalent may vary between apparatus due to differences inconstruction design, tubing size, chamber size, etc.

Expansion chamber 170 may include one or more oxygen sensors capable ofbeing used to determine an oxygen concentration of gas passing throughthe chamber. In an embodiment, the oxygen concentration of gas passingthrough expansion chamber 170 is assessed using oxygen sensor 165. Anoxygen sensor is a device capable of detecting oxygen in a gas. Examplesof oxygen sensors include, but are not limited to, ultrasonic oxygensensors, electrical oxygen sensors, and optical oxygen sensors. In oneembodiment, oxygen sensor 165 is an ultrasonic oxygen sensor thatincludes ultrasonic emitter 166 and ultrasonic receiver 168. In someembodiments, ultrasonic emitter 166 may include multiple ultrasonicemitters and ultrasonic receiver 168 may include multiple ultrasonicreceivers. In embodiments having multiple emitters/receivers, themultiple ultrasonic emitters and multiple ultrasonic receivers may beaxially aligned (e.g., across the gas mixture flow path which may beperpendicular to the axial alignment).

In use, an ultrasonic sound wave (from emitter 166) may be directedthrough oxygen enriched gas disposed in chamber 170 to receiver 168.Ultrasonic sensor assembly may be based on detecting the speed of soundthrough the gas mixture to determine the composition of the gas mixture(e.g., the speed of sound is different in nitrogen and oxygen). In amixture of the two gases, the speed of sound through the mixture may bean intermediate value proportional to the relative amounts of each gasin the mixture. In use, the sound at the receiver 168 is slightly out ofphase with the sound sent from emitter 166. This phase shift is due tothe relatively slow velocity of sound through a gas medium as comparedwith the relatively fast speed of the electronic pulse through wire. Thephase shift, then, is proportional to the distance between the emitterand the receiver and the speed of sound through the expansion chamber.The density of the gas in the chamber affects the speed of sound throughthe chamber and the density is proportional to the ratio of oxygen tonitrogen in the chamber. Therefore, the phase shift can be used tomeasure the concentration of oxygen in the expansion chamber. In thismanner the relative concentration of oxygen in the accumulation chambermay be assessed as a function of one or more properties of a detectedsound wave traveling through the accumulation chamber.

In some embodiments, multiple emitters 166 and receivers 168 may beused. The readings from the emitters 166 and receivers 168 may beaveraged to cancel errors that may be inherent in turbulent flowsystems. In some embodiments, the presence of other gases may also bedetected by measuring the transit time and comparing the measuredtransit time to predetermined transit times for other gases and/ormixtures of gases.

The sensitivity of the ultrasonic sensor system may be increased byincreasing the distance between emitter 166 and receiver 168, forexample to allow several sound wave cycles to occur between emitter 166and the receiver 168. In some embodiments, if at least two sound cyclesare present, the influence of structural changes of the transducer maybe reduced by measuring the phase shift relative to a fixed reference attwo points in time. If the earlier phase shift is subtracted from thelater phase shift, the shift caused by thermal expansion of expansionchamber 170 may be reduced or cancelled. The shift caused by a change ofthe distance between emitter 166 and receiver 168 may be theapproximately the same at the measuring intervals, whereas a changeowing to a change in oxygen concentration may be cumulative. In someembodiments, the shift measured at a later time may be multiplied by thenumber of intervening cycles and compared to the shift between twoadjacent cycles. Further details regarding sensing of oxygen in theexpansion chamber may be found, for example, in U.S. Published PatentApplication No. 2009-0065007, published Mar. 12, 2009, and entitled“Oxygen Concentrator Apparatus and Method, which is incorporated hereinby reference.

Flow rate sensor 185 may be used to determine the flow rate of gasflowing through the outlet system. Flow rate sensors that may be usedinclude, but are not limited to: diaphragm/bellows flow meters; rotaryflow meters (e.g. Hall Effect flow meters); turbine flow meters; orificeflow meters; and ultrasonic flow meters. Flow rate sensor 185 may becoupled to controller 400. The rate of gas flowing through the outletsystem may be an indication of the breathing volume of the user. Changesin the flow rate of gas flowing through the outlet system may also beused to determine a breathing rate of the user. Controller 400 maycontrol actuation of supply valve 160 based on the breathing rate and/orbreathing volume of the user, as assessed by flow rate sensor 185

In some embodiments, ultrasonic sensor system 165 and, for example, flowrate sensor 185 may provide a measurement of an actual amount of oxygenbeing provided. For example, follow rate sensor 185 may measure a volumeof gas (based on flow rate) provided and ultrasonic sensor system 165may provide the concentration of oxygen of the gas provided. These twomeasurements together may be used by controller 400 to determine anapproximation of the actual amount of oxygen provided to the user.

Oxygen enriched gas passes through flow meter 185 to filter 187. Filter187 removes bacteria, dust, granule particles, etc. prior to providingthe oxygen enriched gas to the user. The filtered oxygen enriched gaspasses through filter 187 to connector 190. Connector 190 may be a “Y”connector coupling the outlet of filter 187 to pressure sensor 194 andoutlet conduit 192. Pressure sensor 194 may be used to monitor thepressure of the gas passing through conduit 192 to the user. Changes inpressure, sensed by pressure sensor 194, may be used to determine abreathing rate of a user, as well as the onset of inhalation. Controller400 may control actuation of supply valve 160 based on the breathingrate and/or onset of inhalation of the user, as assessed by pressuresensor 194. In an embodiment, controller 400 may control actuation ofsupply valve 160 based on information provided by flow rate sensor 185and pressure sensor 194.

Oxygen enriched gas may be provided to a user through conduit 192. In anembodiment, conduit 192 may be a silicone tube. Conduit 192 may becoupled to a user using an airway coupling member 196, as depicted inFIG. 3. Airway coupling member 196 may be any device capable ofproviding the oxygen enriched gas to nasal cavities or oral cavities.Examples of airway coupling members include, but are not limited to:nasal masks, nasal pillows, nasal prongs, nasal cannulas, andmouthpieces. A nasal cannula airway delivery device is depicted in FIG.3. During use, oxygen enriched gas from oxygen concentrator system 100is provided to the user through conduit 192 and airway coupling member196. Airway coupling member 196 is positioned proximate to a user'sairway (e.g., proximate to the user's mouth and or nose) to allowdelivery of the oxygen enriched gas to the user while allowing the userto breath air from the surroundings.

Canister System

Oxygen concentrator system 100 may include at least two canisters, eachcanister including a gas separation adsorbent. The canisters of oxygenconcentrator system 100 may be disposed formed from a molded housing. Inan embodiment, canister system 300 includes two housing components 310and 510, as depicted in FIG. 4. The housing components 310 and 510 maybe formed separately and then coupled together. In some embodiments,housing components 310 and 510 may be injection molded or compressionmolded. Housing components 310 and 510 may be made from a thermoplasticpolymer such as polycarbonate, methylene carbide, polystyrene,acrylonitrile butadiene styrene (ABS), polypropylene, polyethylene, orpolyvinyl chloride. In another embodiment, housing components 310 and510 may be made of a thermoset plastic or metal (such as stainless steelor a light-weight aluminum alloy). Lightweight materials may be used toreduce the weight of the oxygen concentrator 100. In some embodiments,the two housings 310 and 510 may be fastened together using screws orbolts. Alternatively, housing components 310 and 510 may be solventwelded together.

As shown, valve seats 320, 322, 324, and 326 and air pathways 330 and332 may be integrated into the housing component 310 to reduce thenumber of sealed connections needed throughout the air flow of theoxygen concentrator 100. In various embodiments, the housing components310 and 410 of the oxygen concentrator 100 may form a two-part moldedplastic frame that defines two canisters 302 and 304 and accumulationchamber 106.

Air pathways/tubing between different sections in housing components 310and 510 may take the form of molded conduits. Conduits in the form ofmolded channels for air pathways may occupy multiple planes in housingcomponents 310 and 510. For example, the molded air conduits may beformed at different depths and at different x,y,z positions in housingcomponents 310 and 510. In some embodiments, a majority or substantiallyall of the conduits may be integrated into the housing components 310and 510 to reduce potential leak points.

In some embodiments, prior to coupling housing components 310 and 510together, O-rings may be placed between various points of housingcomponents 310 and 510 to ensure that the housing components areproperly sealed. In some embodiments, components may be integratedand/or coupled separately to housing components 310 and 510. Forexample, tubing, flow restrictors (e.g., press fit flow restrictors),oxygen sensors, gas separation adsorbents 139, check valves, plugs,processors, power supplies, etc. may be coupled to housing components510 and 410 before and/or after the housing components are coupledtogether.

In some embodiments, apertures 337 leading to the exterior of housingcomponents 310 and 410 may be used to insert devices such as flowrestrictors. Apertures may also be used for increased moldability. Oneor more of the apertures may be plugged after molding (e.g., with aplastic plug). In some embodiments, flow restrictors may be insertedinto passages prior to inserting plug to seal the passage. Press fitflow restrictors may have diameters that may allow a friction fitbetween the press fit flow restrictors and their respective apertures.In some embodiments, an adhesive may be added to the exterior of thepress fit flow restrictors to hold the press fit flow restrictors inplace once inserted. In some embodiments, the plugs may have a frictionfit with their respective tubes (or may have an adhesive applied totheir outer surface). The press fit flow restrictors and/or othercomponents may be inserted and pressed into their respective aperturesusing a narrow tip tool or rod (e.g., with a diameter less than thediameter of the respective aperture). In some embodiments, the press fitflow restrictors may be inserted into their respective tubes until theyabut a feature in the tube to halt their insertion. For example, thefeature may include a reduction in radius. Other features are alsocontemplated (e.g., a bump in the side of the tubing, threads, etc.). Insome embodiments, press fit flow restrictors may be molded into thehousing components (e.g., as narrow tube segments).

In some embodiments, spring baffle 129 may be placed into respectivecanister receiving portions of housing component 310 and 510 with thespring side of the baffle 129 facing the exit of the canister. Springbaffle 129 may apply force to gas separation adsorbent 139 in thecanister while also assisting in preventing gas separation adsorbent 139from entering the exit apertures. Use of a spring baffle 129 may keepthe gas separation adsorbent compact while also allowing for expansion(e.g., thermal expansion). Keeping the gas separation adsorbent 139compact may prevent the gas separation adsorbent from breaking duringmovement of the oxygen concentrator system 100).

In some embodiments, pressurized air from the compression system 200 mayenter air inlet 306. Air inlet 306 is coupled to inlet conduit 330. Airenters housing component 310 through inlet 306 travels through conduit330, and then to valve seats 322 and 324. FIG. 5 and FIG. 6 depict anend view of housing 310. FIG. 5, depicts an end view of housing 310prior to fitting valves to housing 310. FIG. 6 depicts an end view ofhousing 310 with the valves fitted to the housing 310. Valve seats 322and 324 are configured to receive inlet valves 122 and 124 respectively.Inlet valve 122 is coupled to canister 302 and inlet valve 124 iscoupled to canister 304. Housing 310 also includes valve seats 332 and334 configured to receive outlet valves 132 and 134 respectively. Outletvalve 132 is coupled to canister 302 and outlet valve 134 is coupled tocanister 304. Inlet valves 122/124 are used to control the passage ofair from conduit 330 to the respective canisters.

In an embodiment, pressurized air is sent into one of canisters 302 or304 while the other canister is being vented. For example, during use,inlet valve 122 is opened while inlet valve 124 is closed. Pressurizedair from compression system 200 is forced into canister 302, while beinginhibited from entering canister 304 by inlet valve 124. Duringpressurization of canister 302, outlet valve 132 is closed and outletvalve 134 is opened. Similar to the inlet valves, outlet valves 132 and134 are operated out of phase with each other. Each inlet valve seat 322includes an opening 375 that passes through housing 310 into canister302. Similarly valve seat 324 includes an opening 325 that passesthrough housing 310 into canister 302. Air from conduit 330 passesthrough openings 323, or 325 if the respective valve (322 or 324) isopen, and enters a canister.

Check valves 142 and 144 (See, FIG. 4) are coupled to canisters 302 and304, respectively. Check valves 142 and 144 are one way valves that arepassively operated by the pressure differentials that occur as thecanisters are pressurized and vented. Oxygen enriched gas, produced incanisters 302 and 304 pass from the canister into openings 542 and 544of housing 410. A passage (not shown) links openings 542 and 544 toconduits 342 and 344, respectively. Oxygen enriched gas produced incanister 302 passes from the canister though opening 542 and intoconduit 342 when the pressure in the canister is sufficient to opencheck valve 142. When check valve 142 is open, oxygen enriched gas flowsthrough conduit 342 toward the end of housing 310. Similarly, oxygenenriched gas produced in canister 304 passes from the canister thoughopening 544 and into conduit 344 when the pressure in the canister issufficient to open check valve 144. When check valve 144 is open, oxygenenriched gas flows through conduit 344 toward the end of housing 310.

Oxygen enriched gas from either canister, travels through conduit 342 or344 and enters conduit 346 formed in housing 310. Conduit 346 includesopenings that couple the conduit to conduit 342, conduit 344 andaccumulator 106. Thus oxygen enriched gas, produced in canister 302 or304, travels to conduit 346 and passes into accumulator 106.

After some time the gas separation adsorbent will become saturated withnitrogen and will be unable to separate significant amounts of nitrogenfrom incoming air. When the gas separation adsorbent in a canisterreaches this saturation point, the inflow of compressed air is stoppedand the canister is vented to remove nitrogen. Canister 302 is vented byclosing inlet valve 122 and opening outlet valve 132. Outlet valve 132releases the vented gas from canister 302 into the volume defined by theend of housing 310. Foam material may cover the end of housing 310 toreduce the sound made by release of gases from the canisters. Similarly,canister 304 is vented by closing inlet valve 124 and opening outletvalve 134. Outlet valve 134 releases the vented gas from canister 304into the volume defined by the end of housing 310.

While canister 302 is being vented, canister 304 is pressurized toproduce oxygen enriched gas in the same manner described above.Pressurization of canister 304 is achieved by closing outlet valve 134and opening inlet valve 124. The oxygen enriched gas exits canister 304through check valve 144.

In an exemplary embodiment, a portion of the oxygen enriched gas may betransferred from canister 302 to canister 304 when canister 304 is beingvented of nitrogen. Transfer of oxygen enriched gas from canister 302 tocanister 304, during venting of canister 304, helps to further purgenitrogen (and other gases) from the canister. Flow of oxygen enrichedgas between the canisters is controlled using flow restrictors andvalves, as depicted in FIG. 1. Three conduits are formed in housing 510for use in transferring oxygen enriched gas between canisters. As shownin FIG. 7, conduit 530 couples canister 302 to canister 304. Flowrestrictor 151 (not shown) is disposed in conduit 530, between canister302 and canister 304 to restrict flow of oxygen enriched gas during use.Conduit 532 also couples canister 302 to 304. Conduit 532 is coupled tovalve seat 552 which receives valve 152, as shown in FIG. 8. Flowrestrictor 153 (not shown) is disposed in conduit 532, between canister302 and 304. Conduit 534 also couples canister 302 to 304. Conduit 534is coupled to valve seat 554 which receives valve 154, as shown in FIG.8. Flow restrictor 155 (not shown) is disposed in conduit 434, betweencanister 302 and 304. The pair of equalization/vent valves 152/154 workwith flow restrictors 153 and 155 to optimize the air flow balancebetween the two canisters.

Oxygen enriched gas in accumulator 106 passes through supply valve 160into expansion chamber 170 which is formed in housing 510. An opening(not shown) in housing 510 couples accumulator 106 to supply valve 160.In an embodiment, expansion chamber may include one or more devicescapable of being used to determine an oxygen concentration of gaspassing through the chamber.

Controller System

Operation of oxygen concentrator system 100 may be performedautomatically using an internal controller 400 coupled to variouscomponents of the oxygen concentrator system, as described herein.Controller 400 includes one or more processors 410 and internal memory420, as depicted in FIG. 1. Methods used to operate and monitor oxygenconcentrator system 100 may be implemented by program instructionsstored in memory 420 or a carrier medium coupled to controller 400, andexecuted by one or more processors 410. A non-transitory memory mediummay include any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a Compact Disc Read Only Memory (CD-ROM), floppy disks, or tapedevice; a computer system memory or random access memory such as DynamicRandom Access Memory (DRAM), Double Data Rate Random Access Memory (DDRRAM), Static Random Access Memory (SRAM), Extended Data Out RandomAccess Memory (EDO RAM), Rambus Random Access Memory (RAM), etc.; or anon-volatile memory such as a magnetic media, e.g., a hard drive, oroptical storage. The memory medium may comprise other types of memory aswell, or combinations thereof. In addition, the memory medium may belocated in a first computer in which the programs are executed, or maybe located in a second different computer that connects to the firstcomputer over a network, such as the Internet. In the latter instance,the second computer may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums that may reside in different locations, e.g., indifferent computers that are connected over a network.

In some embodiments, controller 400 includes processor 410 thatincludes, for example, one or more field programmable gate arrays(FPGAs), microcontrollers, etc. included on a circuit board disposed inoxygen concentrator system 100. Processor 410 is capable of executingprogramming instructions stored in memory 420. In some embodiments,programming instructions may be built into processor 410 such that amemory external to the processor may not be separately accessed (i.e.,the memory 420 may be internal to the processor 410).

Processor 410 may be coupled to various components of oxygenconcentrator system 100, including, but not limited to compressionsystem 200, one or more of the valves used to control fluid flow throughthe system (e.g., valves 122, 124, 132, 134, 152, 154, 160, orcombinations thereof), oxygen sensor 165, pressure sensor 194, flow ratemonitor 180, temperature sensors, fans, and any other component that maybe electrically controlled. In some embodiments, a separate processor(and/or memory) may be coupled to one or more of the components.

Controller 400 is programmed to operate oxygen concentrator system 100and is further programmed to monitor the oxygen concentrator system formalfunction states. For example, in one embodiment, controller 400 isprogrammed to trigger an alarm if the system is operating and nobreathing is detected by the user for a predetermined amount of time.For example, if controller 400 does not detect a breath for a period of75 seconds, an alarm LED may be lit and/or an audible alarm may besounded. If the user has truly stopped breathing, for example, during asleep apnea episode, the alarm may be sufficient to awaken the user,causing the user to resume breathing. The action of breathing may besufficient for controller 400 to reset this alarm function.Alternatively, if the system is accidently left on when output conduit192 is removed from the user, the alarm may serve as a reminder for theuser to turn oxygen concentrator system 100 off.

Controller 400 is further coupled to oxygen sensor 165, and may beprogrammed for continuous or periodic monitoring of the oxygenconcentration of the oxygen enriched gas passing through expansionchamber 170. A minimum oxygen concentration threshold may be programmedinto controller 400, such that the controller lights an LED visual alarmand/or an audible alarm to warn the patient of the low concentration ofoxygen.

Controller 400 is also coupled to internal power supply 180 and iscapable of monitoring the level of charge of the internal power supply.A minimum voltage and/or current threshold may be programmed intocontroller 400, such that the controller lights an LED visual alarmand/or an audible alarm to warn the patient of low power condition. Thealarms may be activated intermittently and at an increasing frequency asthe battery approaches zero usable charge.

Further functions of controller 400 are described in detail in othersections of this disclosure.

A user may have a low breathing rate or depth if relatively inactive(e.g., asleep, sitting, etc.) as assessed by comparing the detectedbreathing rate or depth to a threshold. The user may have a highbreathing rate or depth if relatively active (e.g., walking, exercising,etc.). An active/sleep mode may be assessed automatically and/or theuser may manually indicate a respective active or sleep mode by apressing button for active mode and another button for sleep mode. Insome embodiments, a user may toggle a switch from active mode, normalmode, or sedentary mode. The adjustments made by the oxygen concentratorsystem in response to activating active mode or sleep mode are describedin more detail herein.

Methods of Delivery of Oxygen Enriched Gas

The main use of an oxygen concentrator system is to provide supplementaloxygen to a user. Generally, the amount of supplemental oxygen to beprovided is assessed by a physician. Typical prescribed amounts ofsupplemental oxygen may range from about 1 LPM to up to about 10 LPM.The most commonly prescribed amounts are 1 LPM, 2 LPM, 3 LPM, and 4 LPM.Generally, oxygen enriched gas is provided to the use during a breathingcycle to meet the prescription requirement of the user. As used hereinthe term “breathing cycle” refers to an inhalation followed by anexhalation of a person.

In order to minimize the amount of oxygen enriched gas that is needed tobe produced to meet the prescribed amounts, controller 400 may beprogrammed to time delivery of the oxygen enriched gas with the user'sinhalations. Releasing the oxygen enriched gas to the user as the userinhales may prevent unnecessary oxygen generation (further reducingpower requirements) by not releasing oxygen, for example, when the useris exhaling. Reducing the amount of oxygen required may effectivelyreduce the amount of air compressing needed for oxygen concentrator 100(and subsequently may reduce the power demand from the compressors).

Oxygen enriched gas, produced by oxygen concentrator system 100 isstored in an oxygen accumulator 106 and released to the user as the userinhales. The amount of oxygen enriched gas provided by the oxygenconcentrator system is controlled, in part, by supply valve 160. In anembodiment, supply valve 160 is opened for a sufficient amount of timeto provide the appropriate amount of oxygen enriched gas, as assessed bycontroller 400, to the user. In order to minimize the amount of oxygenrequired to meet the prescription requirements of a user, the oxygenenriched gas may be provided in a bolus when a user's inhalation isfirst detected. For example, the bolus of oxygen enriched gas may beprovided in the first few milliseconds of a user's inhalation.

In an embodiment, pressure sensor 194 and/or flow rate sensor 185 may beused to determine the onset of inhalation by the user. For example, theuser's inhalation may be detected by using pressure sensor 194. In use,a conduit for providing oxygen enriched gas is coupled to a user's noseand/or mouth (e.g., using a nasal cannula or a face mask). At the onsetof an inhalation, the user begins to draw air into their body throughthe nose and/or mouth. As the air is drawn in, a negative pressure isgenerated at the end of the conduit, due, in part, to the venturi actionof the air being drawn across the end of the delivery conduit. Pressuresensor 194 may be operable to create a signal when a drop in pressure isdetected, to signal the onset of inhalation. Upon detection of the onsetof inhalation, supply valve 160 is controlled to release a bolus ofoxygen enriched gas from the accumulator 106.

In some embodiments, pressure sensor 194 may provide a signal that isproportional to the amount of positive or negative pressure applied to asensing surface. The amount of the pressure change detected by pressuresensor 194 may be used to refine the amount of oxygen enriched gas beingprovided to the user. For example, if a large negative pressure changeis detected by pressure sensor 194, the volume of oxygen enriched gasprovided to the user may be increased to take into account the increasedvolume of gas being inhaled by the user. If a smaller negative pressureis detected, the volume of oxygen enriched gas provided to the user maybe decreased to take into account the decreased volume of gas beinginhaled by the user. A positive change in the pressure indicates anexhalation by the user and is generally a time that release of oxygenenriched gas is discontinued. Generally while a positive pressure changeis sensed, valve 160 remains closed until the next onset of inhalation.

In some embodiments, the sensitivity of the pressure sensor 194 may beaffected by the physical distance of the pressure sensor 194 from theuser, especially if the pressure sensor is located in oxygenconcentrator system 100 and the pressure difference is detected throughthe tubing coupling the oxygen concentrator system to the user. In someembodiments, the pressure sensor may be placed in the airway deliverydevice used to provide the oxygen enriched gas to the user. A signalfrom the pressure sensor may be provided to controller 400 in the oxygenconcentrator 100 electronically via a wire or through telemetry such asthrough BLUETOOTH® (Bluetooth, SIG, Inc. Kirkland, Wash.) or otherwireless technology.

In an embodiment, the user's inhalation may be detected by using flowrate sensor 185. In use, a conduit for providing oxygen enriched gas iscoupled to a user's nose and/or mouth (e.g., using a nasal cannula orface mask). At the onset of an inhalation, the user begins to draw airinto their body through the nose and/or mouth. As the air is drawn in,an increase in flow of gas passing through conduit is created. Flow ratesensor 185 may be operable to create a signal when an increase in flowrate is detected, to signal the onset of inhalation. Upon detection ofthe onset of inhalation, supply valve 160 is controlled to release abolus of oxygen enriched gas from the accumulator 106.

A user breathing at a rate of 30 breaths per minute (BPM) during anactive state (e.g., walking, exercising, etc.) may consume two andone-half times as much oxygen as a user who is breathing at 12 BPMduring a sedentary state (e.g., asleep, sitting, etc.). Pressure sensor194 and/or flow rate sensor 185 may be used to determine the breathingrate of the user. Controller 400 may process information received frompressure sensor 194 and/or flow rate sensor 185 and determine abreathing rate based on the frequency of the onset of inhalation. Thedetected breathing rate of the user may be used to adjust the bolus ofoxygen enriched gas. The volume of the bolus of oxygen enriched gas maybe increased as the users breathing rate increase, and may be decreasedas the users breathing rate decreases. Controller 400 may automaticallyadjust the bolus based on the detected activity state of the user.Alternatively, the user may manually indicate a respective active orsedentary mode by selecting the appropriate option on the control panelof the oxygen concentrator. Alternatively, a user may operate controller400 from a remote electronic device. For example, a user may operate thecontroller using a smart phone or tablet device.

In some embodiments, if the user's current activity level as assessedusing the detected user's breathing rate exceeds a predeterminedthreshold, controller 400 may implement an alarm (e.g., visual and/oraudio) to warn the user that the current breathing rate is exceeding thedelivery capacity of the oxygen concentrator system. For example, thethreshold may be set at 20 breaths per minute.

Methods of determining the breathing rate of a user typically count thenumber of breathes taken by the user over a pre-determined time andcalculate the breathing rate. When determining the breathing rate of auser, all breaths measured during the pre-determined time period aretypically used to calculate the breathing rate. Such a method, however,can lead to significant errors due to sudden changes in the breathingrate of the user. For example, while sleeping it is know that the timesbetween breaths may vary greatly for an individual. Breathing patternsnormally change during sleep. During deep sleep, breathing slows andbecomes lighter as the body rests. During light sleep and REM, breathingcan resemble breathing patterns of the person when awake. Periods ofheavy breathing may also occur during dreams. Changes in breathing ratecan occur quickly while a user is sleeping and even during awakeperiods. If the delivery of oxygen enriched gas is not adapted to thebreathing patterns of the user properly, oxygen enriched gas may bewasted, by providing the oxygen enriched gas for too long, or may beinsufficient, if the oxygen enriched gas is provided for too short aperiod.

Attempts have been made to take into account the erratic breathing of auser. For example, U.S. Pat. No. 7,841,343 to Deane et al. (“Deane”)described the use of a blind time to help compensate for erraticbreathing. Specifically, Deane teaches that after a bolus of oxygenenriched gas is delivered to a user, a controller enters a blind time.During this blind time the controller will not accept any triggers todeliver oxygen enriched gas. This time may range from 0.5 to 3 secondsafter the bolus is delivered. After this blind time has elapsed thecontroller sets the inspiration breath pressure threshold to a low leveland gradually increases the sensitivity until a breath is detected.According to Deane, this helps to vary the bolus delivery in response tochanges in the users breathing.

The method of Deane relies on a blind time in which no breaths aredetected. Thus, if the user starts breathing rapidly, shortly after thedelivery of a bolus of oxygen enriched gas, the method of Deane may bedelayed in reacting to the change in breathing. In the worst casescenario, the user may change to a breathing rate in which every otherbreath falls within the blind time, leading to the false indication thatthe user is breathing at a breathing rate that is half the actualbreathing rate. Such a situation can lead to oxygen depravity in theindividual due to an insufficient amount of oxygen being supplied to theuser.

Applicant has devised an improved method of determining a breathingrate, and controlling the inspiration breath pressure threshold based onthe determined breathings. In an embodiment, the controller determinesthe breathing rate based on measuring a predetermined number of breaths(at least three) and discarding information related to the last breathmeasured. In this method the time between the penultimate breath and thelast breath is not used to determine the average breathing rate. Thebreathing rate, determined using the information collected from theremaining breaths, was found to give a more accurate indication of thecurrent breathing rate of the user. Such a method also provides a way totake into account erratic breathing patterns without having to resort tothe extreme measure of creating artificial “blind times,” as discussedin Deane.

Over a period of time, controller 400 may collect and store the numberof breaths. Based on the number of breaths, or the average time betweenbreaths, over the period of time a breathing rate may be calculated. Insome embodiments, the period of time is divided into equal time units.The number of breaths, or the average time between breaths, isdetermined in each time unit for the set period of time. The number ofbreaths, or average time between breaths, per time unit is used todetermine a breathing rate. In some embodiments, the breathing rate inthe last time unit is not used to determine if the delivery parametersshould be changed. For example, if a period of time is broken up into 5equal time units, the breathing rate determined for the last time unitis not used to determine an average breathing rate (for example, averagebreaths per minute).

For example, controller 400 may collect the number of breaths over a 5minute period of time. During the 5 minutes, a user may have a breathingrate of 15 breaths per minute (“BPM”) for the first minute of the 5minute time period, 10 BPM during the second minute of the 5 minute timeperiod, 25 BPM during the third minute of the 5 minute time period, 30BPM during the fourth minute of the 5 minute time period, and 40 BPMduring the fifth minute of the 5 minute time period. The 40 BPM may beignored and the remaining breaths averaged (for example, to determine anaverage breathing rate of 20 BPM. The breathing rate determined duringthe last minute of the 5 minute time period may be used for averaging ofthe next 5 minute time period. For example the last minute of the 5minute time period may be used as the first minute of the next fiveminute time period. Alternatively, the five minute time period analyzedmay be shifted by a minute. In this case, the second minute of the fiveminute period just analyzed becomes the first minute of the next fiveminute period. The fifth minute (ignored in the first breathing rateanalysis), becomes the fourth minute of the next breathing rateanalysis. In either case the last minute is ignored in the breathingrate analysis.

In another embodiment, the breathing rate may be determined bymonitoring the time between each breath for at least three breaths. Insome embodiments, the times between each of four, five, six, seven,eight, nine, ten, fifteen, sixteen, seventeen, or twenty successivebreaths are measured and used to determine an average breathing rate. Inthis method the time between the penultimate breath and the last breathis ignored, with the breathing rate based on the time between thebreaths up to the penultimate breath. For example, if 5 successivebreaths are used to determine a breathing rate, the time between the4^(th) and 5^(th) breath is discarded when determining the breathingrate. For example if the following times between breaths are obtained:1^(st)-2^(nd): 4.5 sec., 2^(nd)-3^(rd): 4.7 sec, 3^(rd)-4^(th)—4.2 sec,4^(th)-5^(th): 5.2 sec, the average time between breaths is determinedby averaging the first three times (4.5 sec, 4.7 sec, and 4.2 sec) andignoring the last breath (5.2 sec). In this manner the average timebetween breaths is 4.47, giving an average breathing rate of 13.4breathes per minute.

Using the average breathing rate, the inspiration breath pressurethreshold may be adjusted relative to the current inspiration breathpressure threshold. Controller 400 may determine that the averagebreathing rate has changed from less than 15 breaths per minute togreater than 15 breaths per minute. Controller 400 may send anelectronic signal to pressure sensor 194 that raises the thresholdbreath pressure inspiration relative to the current inspiration breathpressure threshold. When the determined average breathing rate changesfrom greater than 10 breaths per minute to less than 10 breaths perminute, controller 400 may send an electronic signal to the pressuresensor 194 that lowers the inspiration breath pressure thresholdrelative to the current inspiration breath pressure threshold.Controller 400 may determine that the average breathing rate is between10 breaths per minute and 15 breaths per minute, and determine that nochange in the current inspiration breath pressure threshold isnecessary. If the average breathing rate is less than 5 breaths perminute then controller 400 may trigger an alarm. If the inspirationbreath pressure threshold has been lowered relative to the currentinspiration breath pressure threshold and no inspiration breath pressureis detected after a period of time (for example, 75 seconds), thencontroller 400 may trigger an alarm.

In another embodiment, the change in the inspiration breath pressurethreshold may be adjusted by looking at the change in breathing rateover a predetermined period of time. For example, a change in breathingrate can be monitored by creating successive groupings of three or morebreaths. For each successive grouping of three or more breaths, thebreathing rate is determined (e.g., by calculating the breathing ratebased on an average time between each breath in the grouping). Thebreathing rate from each grouping is compared to the next grouping todetermine how the breathing rate is changing. If the breathing rate isincreasing over three or more successive groupings (e.g., the breathingrate increases in at least two of the groupings), the controller mayincrease the inspiration breath pressure threshold. If the breathingrate is decreasing over three or more successive groupings (e.g., thebreathing rate decreases in at least two of the groupings), thecontroller may lower the inspiration breath pressure threshold.

In a specific example, the time between each of seventeen successivebreaths is measured. The breaths are then divided into four groupings,with each grouping having the inhalation times for four successivebreaths. The groupings would then look as shown below, the number inparenthesis refers to the time between the breaths:

1 (5.8 s) 2 (5.0 s) 3 (4.2 s) 4 BPM = 12 (4.0 s) 5 (3.5 s) 6 (3.5 s) 7(3.0 s) 8 BPM = 17 (3.0 s) 9 (3.4 s) 10 (3.6 s) 11 (3.5 s) 12 BPM = 18(2.6 s) 13 (2.6 s) 14 (2.4 s) 15 (2.0 s) 16 BPM = 25 (2.7 s) 17The last time (the time between breath 16 and 17, is not used todetermine the breathing rate. In the above example, the first grouping(breaths 1-4) exhibits a breathing rate of 12 BPM. The second groupingexhibits a breathing rate of 17 BPM, which shows that the subjectsbreathing rate is increasing. Instead of changing the inspiration breathpressure threshold, the controller goes into a “watch” mode. In the“watch” mode the controller is alerted that a change in the inspirationbreath pressure threshold may be needed. The controller then looks atthe third grouping. The third grouping exhibits a breathing rate of 18BPM. A breathing rate that is within +/−2 of the previous breathingrate, is not considered to have changed. Since the breathing rate hasnot changed (as defined above) from the second grouping to the thirdgrouping, the controller remains in watch mode. The controller thenlooks at the change between the third and fourth groupings. The fourthgrouping exhibits a breathing rate of 25 BPM. Since the controller hasnow seen a second increase among the four groupings measured, thecontroller increase the inspiration breath pressure threshold. Thecontroller will continue to take additional groupings (in this example,of four successive breaths, excluding the last breath taken) andcontinue to evaluate whether the inspiration breath pressure thresholdshould be adjusted.

In some embodiments, rather than ignoring the last breath, the lastgrouping is ignored. For example, in the above example, the controllerbases the decision to change the inspiration breath pressure thresholdbased on the first three groupings, ignoring the last (4^(th)) grouping.Under these circumstances, the inspiration breath pressure threshold isnot changed until additional groupings are taken and it is determined ifthe increase in breathing rate is continued.

In alternate embodiments, the controller may base decisions on theactual BPM rather than the change in BPM. For example, if the BPMchanges to less than 10 breaths per minute in a grouping, the controllermay go into a watch mode. If the BPM remains below 10 BPM in one of thenext two groupings, the controller may send an electronic signal to thepressure sensor that lowers the inspiration breath pressure thresholdrelative to the current inspiration breath pressure threshold. If theBPM is between 10 breaths per minute and 15 breaths per minute, then nochange is made to the inspiration breath pressure threshold. If the BPMchanges to more than 15 breaths per minute in a grouping, the controllermay go into a watch mode. If the BPM remains above 15 BPM in one of thenext two groupings, the controller may send an electronic signal to thepressure sensor that increase the inspiration breath pressure thresholdrelative to the current inspiration breath pressure threshold. In thisembodiment, as discussed above, the last breath detected or the lastgrouping measured may be ignored when determining if the inspirationbreath pressure threshold should be changed.

In some embodiments, it is not necessary to calculate the breathingrate, but instead the time between breaths may be used in a decisionmaking process. A flow chart of a process of adjusting the inspirationbreath pressure threshold is shown in FIG. 10. During use, the timesbetween at least three consecutives breaths is measured. When the timebetween, for example, the fourth breath and the fifth breath ismeasured, the controller determines if a change in the inspirationbreath pressure threshold is needed. The times between breaths 1 and 2;2 and 3; and 3 and 4 are used to determine the average time betweenbreaths. The time between breath 4 and breath 5 is not used to determinethe average time between breaths. The average time between breaths 1-4is then compared to predetermined values. In one embodiment, the subjectis considered to be in an active state if the average time betweenbreaths is less than 4 seconds. It should be understood that other timescan be used. Thus process therefore includes comparing the average timebetween breaths of the subject to the predetermined active state time.If the average time between breaths of the subject is less than theactive state time, the controller sets the inspiration breath pressurethreshold to a high pressure.

If the average time between breaths of the subject is greater than theactive state time, the controller compares the time to an inactive statetime. In one embodiment, the subject is considered to be in an inactivestate if the average time between breaths is greater than 6 seconds. Itshould be understood that other times can be used. If the average timebetween breaths of the subject is greater than 6 seconds, the controllersets the inspiration breath pressure threshold to a low pressure. If theaverage time between breaths of the subject is between 4 and 6 seconds,the controller does not change the inspiration breath pressurethreshold.

As shown in FIG. 10, when the breath 6 is taken, the process isrepeated, however, the average is now based on the times between breath2 and breath 5. Once the average time between breaths 2-5 is determined,the same process as discussed above is used to determine whether theinspiration breath pressure threshold should be changed, and, if itshould be changed, whether it should be set to a high pressure (active)or a low pressure (inactive). This process may be continued as long asoxygen is being provided to the user.

In some embodiments, controller 400 may send a signal to adjust pressuresensor 194 to adjust the threshold inspiration breath pressure based onthe ratio of the change in absolute pressure with respect to timemonitored over at least three breaths. In some embodiments, the changein absolute pressure with respect to time between each of four, five,six, seven, eight, nine, ten, fifteen or twenty successive breaths aremeasured and used to determine a ratio of change in absolute pressurewith respect to time. Controller 400 may determine a ratio of the changein absolute pressure with respect to time based during a breathingperiod and store the information in a non-transitory medium. Based onthe determined ratio between the change in absolute pressure withrespect to time, controller 400 may send an electronic signal to breathpressure sensor 194 that adjusts the inspiration breath pressurethreshold. If ratio is assessed to be negative, and less than, or equalto, −0.5 controller 400 may send an electronic signal to breath pressuresensor 194 that lowers the inspiration breath pressure thresholdrelative to the current inspiration breath pressure threshold. Forexample, if the ratio is assessed to be about −1.5 to about −0.5, (i.e.,less than or equal to −0.5), controller 400 may send an electronicsignal to breath pressure sensor 194 that lowers the inspiration breathpressure threshold relative to the current inspiration breath pressurethreshold. If the ratio is assessed to be slightly positive or slightlynegative (e.g., between −0.5 to +0.5), controller 400 may send anelectronic signal to breath pressure sensor 194 that keeps theinspiration breath pressure threshold the same as the currentinspiration breath pressure threshold. If the ratio is positive, and,for example, greater than or equal to +0.5, for example, controller 400may send an electronic signal to breath pressure sensor 194 that raisesthe inspiration breath pressure threshold relative to the currentinspiration breath pressure threshold.

In some embodiments, controller 400 may operate the oxygen concentratorbased on the change in the inspiration breath pressure threshold. Thefrequency and/or duration of the provided oxygen enriched gas to theuser relative to the current frequency and/or duration may be adjustedbased on the change in the inspiration breath pressure threshold. Upondetermining that the inspiration breath pressure threshold has beenlowered, the controller 400 may switch the oxygen concentrator to asedentary mode. Controller 400 may switch the oxygen concentrator to anactive mode, when the inspiration breath pressure threshold has beenraised.

In some embodiments, as seen in FIG. 9, the bolus of provided oxygenenriched gas may include two or more pulses. For example, with a oneliter per minute (LPM) delivery rate, the bolus may include two pulses:a first pulse 556 at approximately 7 cubic centimeters and a secondpulse 558 at approximately 3 cubic centimeters. Other delivery rates,pulse sizes, and number of pulses are also contemplated. For example, at2 LPMs, the first pulse may be approximately 14 cubic centimeters and asecond pulse may be approximately 6 cubic centimeters and at 3 LPMs, thefirst pulse may be approximately 21 cubic centimeters and a second pulsemay be approximately 9 cubic centimeters. In some embodiments, thelarger pulse 556 may be provided when the onset of inhalation isdetected (e.g., detected by pressure sensor 194). In some embodiments,the pulses may be provided when the onset of inhalation is detectedand/or may be spread time-wise evenly through the breath. In someembodiments, the pulses may be stair-stepped through the duration of thebreath. In some embodiments, the pulses may be distributed in adifferent pattern. Additional pulses may also be used (e.g., 3, 4, 5,etc. pulses per breath). While the first pulse 556 is shown to beapproximately twice the second pulse 558, in some embodiments, thesecond pulse 558 may be larger than the first pulse 556. In someembodiments, pulse size and length may be controlled by, for example,supply valve 160 which may open and close in a timed sequence to providethe pulses. A bolus with multiple pulses may have a smaller impact on auser than a bolus with a single pulse. The multiple pulses may alsoresult in less drying of a user's nasal passages and less blood oxygendesaturation. The multiple pulses may also result in less oxygen waste.

In some embodiments, the sensitivity of the oxygen concentrator 100 maybe selectively attenuated to reduce false inhalation detections due tomovement of air from a different source (e.g., movement of ambient air).For example, the oxygen concentrator 100 may have two selectablemodes—an active mode and an inactive mode. In some embodiments, the usermay manually select a mode (e.g., through a switch or user interface).In some embodiments, the mode may be automatically selected by theoxygen concentrator 100 based on a detected breathing rate. For example,the oxygen concentrator 100 may use the pressure sensor 194 to detect abreathing rate of the user. If the breathing rate is above a threshold,the oxygen concentrator 100 may operate in an active mode (otherwise,the oxygen concentrator may operate in an inactive mode). Other modesand thresholds are also contemplated.

In some embodiments, in active mode, the sensitivity of the pressuresensor 194 may be mechanically, electronically, or programmaticallyattenuated. For example, during active mode, controller 400 may look fora greater pressure difference to indicate the start of a user breath(e.g., an elevated threshold may be compared to the detected pressuredifference to determine if the bolus of oxygen should be released). Insome embodiments, the pressure sensor 194 may be mechanically altered tobe less sensitive to pressure differences. In some embodiments, anelectronic signal from the pressure sensor may be electronically alteredto ignore small pressure differences. This can be useful when in activemode. In some embodiments, during the inactive mode the sensitivity ofthe pressure sensor may be increased. For example, the controller 400may look for a smaller pressure difference to indicate the start of auser breath (e.g., a smaller threshold may be compared to the detectedpressure difference to determine if the bolus of oxygen should bereleased). In some embodiments, with increased sensitivity, the responsetime for providing the bolus of oxygen during the user's inhalation maybe reduced. The increased sensitivity and smaller response time mayreduce the size of the bolus necessary for a given flow rateequivalence. The reduced bolus size may also reduce the size and powerconsumption of the oxygen concentrator 100.

Providing a Bolus Based on Inhalation Profile

In an embodiment, the bolus profile can be designed to match the profileof a particular user. To do so, an inhalation profile may be generatedbased on information gathered from pressure sensor 194 and flow ratesensor 185. An inhalation profile is assessed based on, one or more ofthe following parameters: the breathing rate of the user; the inhalationvolume of the user; the exhalation volume of the user; the inhalationflow rate of the user; and the exhalation flow rate of the user. Thebreathing rate of the user may be assessed by detecting the onset ofinhalation using pressure sensor 194 or flow rate sensor 185 aspreviously discussed. Inhalation volume may be assessed by measuring thechange in pressure during inhalation and calculating or empiricallyassessing the inhalation volume based on the change in pressure.Alternatively, inhalation volume may be assessed by measuring the flowrate during inhalation and calculating or empirically assessing theinhalation volume based on the flow rate and the length of theinhalation. Exhalation volume may be assessed in a similar manner usingeither positive pressure changes during exhalation, or flow rate andexhalation time. Inhalation flow rate of the user is measured fromshortly after the onset of inhalation. Detection of the end ofinhalation may be from the pressure sensor or the flow rate sensor. Whenonset of inhalation is detected by the pressure sensor, the onset ischaracterized by a drop in pressure. When the pressure begins toincrease, the inhalation is considered complete. When onset ofinhalation is detected by the flow rate sensor, the onset ischaracterized by an increase in the flow rate. When the flow rate beginsto decrease, the inhalation is considered complete.

There is a minimum amount of oxygen necessary for a person to remainconscious. A person who is breathing rapidly is bringing in a lowervolume of air in each breath, and thus, requires less oxygen enrichedgas per inhalation. While there is some variation from patient topatient, this relationship can be used to establish the mean flow ratefor each breath mathematically. By measuring a large population ofpatients, the profile of the relative flow from onset of inhalation tothe onset of exhalation may be established. Using this flow profile as atemplate, the calculated actual flow based on breathing rate can beadjusted mathematically to a calculated actual flow profile. Thisprofile can be used to adjust the opening and closing of the deliveryvalve to create an idealized profile for the patient based on theirbreathing rate. Inhalation profile data gathered from a population ofusers may be used to create an algorithm that makes the appropriateadjustments based on the detected inhalation profile. Alternatively, alook up table may be used to control valve actuation durations and pulsequantities based on a detected inhalation profile.

Measuring the inhalation profile of the patient provides a more accuratebasis for control of the bolus of oxygen enriched gas being provided tothe patient. For example, basing the delivery of oxygen enriched gas onthe onset of inhalation may not take into account differences betweenindividual users. For example, people having a similar breathing ratecan have different inhalation/exhalation volume, inhalation/exhalationflow rates and, thus, different bolus requirements necessary to producethe prescribed amount of oxygen. In one embodiment, an inhalationprofile is created based on the flow rate of air during inhalation andthe duration of inhalation. The inhalation profile can then be used as apredictor of the volume of air taken in by a specific user duringinhalation. Thus, inhalation profile information can be used to modifythe amount of oxygen enriched air provided to the user to ensure thatthe prescribed level of oxygen is received. The amount of oxygenprovided to a user may be adjusted by modifying the frequency and orduration of release of oxygen enriched gas from the accumulator withsupply valve 160. By tracking the inhalation profile of the patientcontroller adjusts the delivery supply valve actuation to idealize thebolus profile to provide the oxygen at the maximum rate without causingwasteful retrograde flow.

In this patent, certain U.S. patents, U.S. patent applications, andother materials (e.g., articles) have been incorporated by reference.The text of such U.S. patents, U.S. patent applications, and othermaterials is, however, only incorporated by reference to the extent thatno conflict exists between such text and the other statements anddrawings set forth herein. In the event of such conflict, then any suchconflicting text in such incorporated by reference U.S. patents, U.S.patent applications, and other materials is specifically notincorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects ofthe invention may be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as embodiments. Elements and materials may besubstituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

1. A method of providing oxygen enriched gas to a user of an oxygenconcentrator, comprising: measuring the time between a plurality ofsuccessive breaths, wherein a breath is determined to begin when a dropin pressure is measured using a pressure sensor coupled to an outlet ofa conduit coupling the user to an oxygen enriched gas source;determining an average breathing rate based on the time between each ofthe successive breaths, wherein the time between the penultimate breathand the last breath is not used to determine the average breathing rate;and setting an inspiration breath pressure threshold for the pressuresensor based on the determined average breathing rate.
 2. The method ofclaim 1 wherein adjusting a threshold inspiration pressure based on theaverage breathing rate comprises lowering the threshold inspirationpressure when the determined average breathing rate changes from greaterthan 10 breaths per minute to less than 10 breaths per minute.
 3. Themethod of claim 1, wherein adjusting a threshold inspiration pressurebased on the average breathing rate comprises increasing the thresholdinspiration pressure when the determined average breathing rate changesfrom less than 15 breaths per minute to greater than 15 breaths perminute.
 4. The method of claim 1, wherein adjusting a thresholdinspiration pressure based on the average breathing rate comprisesmaintaining the inspiration breath pressure threshold at a currentsetting when the average breathing rate is between about 10 breaths perminute and about 15 breaths per minute.
 5. The method of claim 1,wherein the method comprises measuring the time between at least sixsuccessive breaths.
 6. The method of claim 1, further comprisingswitching to an active mode, a sedentary mode, or remaining at thecurrent mode based on the average breathing rate.
 7. The method of claim1, further comprising switching the oxygen concentrator to an activemode, when the average breathing rate comprises at least 15 breaths perminute.
 8. The method of claim 1, further comprising switching theoxygen concentrator to a sedentary mode, when the average breathing ratecomprises less than 10 breaths per minute.
 9. The method of claim 1,wherein adjusting the inspiration breath pressure threshold based on theaverage breathing rate is performed automatically.
 10. The method ofclaim 1, wherein the oxygen enriched gas source is an oxygenconcentrator system.
 11. The method of claim 1, wherein the oxygenenriched gas source is an oxygen tank.
 12. An oxygen concentratorapparatus, comprising: a pressure sensor, the pressure sensor configuredto detect a breath pressure of a user; and a processor operable coupledto the pressure sensor, the processor to execute non-transitory programinstructions, and wherein the program instructions are operable to:automatically measure the time between a plurality of successivebreaths, wherein a breath is determined to begin when a drop in pressureis measured using the pressure sensor; determine an average breathingrate based on the time between each of the successive breaths, whereinthe time between the penultimate breath and the last breath is not usedto determine the average breathing rate; and set an inspiration breathpressure threshold for the pressure sensor based on the determinedaverage breathing rate.
 13. The oxygen concentrator apparatus of claim12, wherein the program instructions are further operable to implementlowering the inspiration breath pressure threshold of the pressuresensor if the determined average breathing rate changes from greaterthan about 10 breaths per minute to less than about 10 breaths perminute.
 14. The oxygen concentrator apparatus of claim 12, wherein theprogram instructions are further operable to implement increasing theinspiration breath pressure threshold if the determined averagebreathing rate changes from less than about 15 breaths per minute togreater than about 15 breaths per minute.
 15. The oxygen concentratorapparatus of claim 12, wherein the inspiration breath pressure thresholdof the pressure sensor is maintained at a current setting if thedetermined average breathing rate is between about 10 breaths per minuteand 15 breaths per minute.
 16. The oxygen concentrator apparatus ofclaim 12, wherein the program instructions are further operable toproduce an alarm or other signal in response to an average breathingrate of less than 5 breaths per min.
 17. The oxygen concentratorapparatus of claim 12, wherein operating the oxygen concentrator basedon the average breathing rate comprises switching to an active mode whenthe breathing rate is at least 15 breaths per min.
 18. The oxygenconcentrator apparatus of claim 12, wherein operating the oxygenconcentrator based on the average breathing rate comprises switching toa sedentary mode when the breathing rate is less than 10 breaths permin.
 19. The oxygen concentrator apparatus of claim 12, furthercomprising an oxygen sensor coupled to the processor, wherein the oxygensensor is capable of detecting oxygen in a gas during use.
 20. Theoxygen concentrator apparatus of claim 12, wherein the oxygenconcentrator weighs less than 5 lbs. 21-61. (canceled)
 62. A method ofproviding oxygen enriched gas to a user of an oxygen concentrator,comprising: measuring the time between a plurality of successivebreaths, wherein a breath is determined to begin when a drop in pressureis measured using a pressure sensor coupled to an outlet of a conduitcoupling the user to an oxygen enriched gas source; creating groupingsof breaths, wherein each grouping comprises at least three successivebreaths; determining an average breathing rate for each grouping basedon the time between each of the successive breaths within the grouping;and setting an inspiration breath pressure threshold for the pressuresensor based on the determined average breathing rate of two or more ofthe groupings. 63-80. (canceled)